Dialysis is a treatment used to support a patient with insufficient renal function. The two principal dialysis methods are hemodialysis and peritoneal dialysis. During hemodialysis (“HD”), the patient's blood is passed through a dialyzer of a dialysis machine while also passing a dialysis solution or dialysate through the dialyzer. A semi-permeable membrane in the dialyzer separates the blood from the dialysate within the dialyzer and allows diffusion and osmosis exchanges to take place between the dialysate and the blood stream. These exchanges across the membrane result in the removal of waste products, including solutes like urea and creatinine, from the blood. These exchanges also regulate the levels of other substances, such as sodium and water, in the blood. In this way, the dialysis machine acts as an artificial kidney for cleansing the blood.
During peritoneal dialysis (“PD”), the patient's peritoneal cavity is periodically infused with dialysate. The membranous lining of the patient's peritoneum acts as a natural semi-permeable membrane that allows diffusion and osmosis exchanges to take place between the solution and the blood stream. These exchanges across the patient's peritoneum result in the removal of waste products, including solutes like urea and creatinine, from the blood, and regulate the levels of other substances, such as sodium and water, in the blood.
Automated PD machines called PD cyclers are designed to control the entire PD process so that it can be performed at home usually overnight without clinical staff in attendance. This process is termed continuous cycler-assisted PD (CCPD). Many PD cyclers are designed to automatically infuse, dwell, and drain dialysate to and from the patient's peritoneal cavity. The treatment typically lasts for several hours, often beginning with an initial drain cycle to empty the peritoneal cavity of used or spent dialysate. The sequence then proceeds through the succession of fill, dwell, and drain phases that follow one after the other. Each phase is called a cycle.
The cyclers are designed to manage a number of bags each typically containing up to 5 liters of dialysate. The dialysate is then pumped by the machine or, in so-called gravity systems, allowed by the machine to flow through a patient line to the patient. But, to avoid thermal shock, the dialysate is heated first to near the patient's body temperature before infusion.
One technique for heating the dialysate is to place a dedicated heater bag on top of a heater tray, equipped with heating coils and a temperature sensor. In this arrangement all fluid going to the patient comes from the heater bag. During a dwell period, the heater bag can be refilled from one of several heater bags connected to the machine and warmed so that it will be ready to supply the next fill to the patient.